1. Field of the Invention
The apparatus of this disclosure is related to the field of pulsed reflection holography and in particular the multiplexing of holographic images of a moving object by rotating the plane of polarization of the coherent lightwave with one intended application being portraiture however, this apparatus could be used to record interference fringes from any kind of moving object moving in close proximity to the recording window of the apparatus. The invention disclosed herein which enables the multiplexing of several holographic images in sequenced intervals of time and space is made possible with the invention of the Hollow Core Photonic Crystal Fiber (HC-PCF) also known as a Birefringent photonic bandgap optical waveguide is described in U.S. Pat. No. 7,321,712 and U.S. Pat. No. 7,805,038. Methods for the production of photonic crystal fibers given in U.S. Pat. No. 6,985,661 and U.S. Pat. No. 7,305,164
2. Description of the Prior Art
A hologram has been described as being a ‘window with a memory’ because the light sensitive recording medium not only records the intensity of the monochromatic light rays that impinge upon the surface of the material but also information as to the phase difference between these monochromatic wavefronts for an instantaneous moment in time.
Not only are the strengths of the monochromatic wavefronts able to be reproduced but also the directions from the points in space from where the wavefronts emanated and in this sense the hologram is a recording of the entire information contained within the microscopic interference fringe pattern and thus, looking at the light sensitive surface is like looking through a window with a memory but more correctly it is a window with a complete memory. The theoretical basis for split beam holography is obtained through an analysis of the intensity distribution function which is as follows; if the field distribution of the reference lightwave impinging upon the recording material is ψr=Ar EXP[−iφr] and if the field distribution of an object lightwave impinging upon the recording material is; ψo=Ao EXP[−iφo] (where Ar; Ao; φr; φo represent the corresponding Amplitude and phase distributions of the lightwaves) then the resultant Intensity distribution I will be;
      I    =                            [                                    ψ              r                        +                          ψ              o                                ]                2            =                                    (                          A              r                        )                    2                +                              (                          A              o                        )                    2                +                              (                                          A                r                            ·                              A                o                                      )                    ⁢          EXP                -                  ⅈ          ⁡                      [                                          φ                o                            -                              φ                r                                      ]                          +                              A            r                    ⁢                                          ⁢                                    A              o                        ·            EXP                          -                  ⅈ          ⁡                      [                                          φ                o                            -                              φ                r                                      ]                                                  ⁢          I      =                                    (                          A              r                        )                    2                +                              (                          A              o                        )                    2                +                  2          ⁢                      (                                          A                r                            ·                              A                o                                      )                    ⁢          EXP                -                              ⅈ            ⁡                          [                                                φ                  o                                -                                  φ                  r                                            ]                                ⁢                                          ⁢          or                                        ⁢          I      =                                    (                          A              r                        )                    2                +                              (                          A              o                        )                    2                +                  2          ⁢                      (                                          A                r                            ·                              A                o                                      )                    ⁢                      cos            ⁡                          (                                                φ                  o                                -                                  φ                  r                                            )                                          This last term is most interesting because it represents the phase difference between the reference and object lightwaves.
In discussing the prior Art it is necessary to mention one of the earliest methods of multiplexing holographic images superimposed on the same position in a recording medium which was to alter the angular direction at which the reference beam is projected onto the recording medium which is known as angular multiplexing. This method does have the drawback that it requires the mechanical movement of optical elements.
In U.S. Pat. No. 3,970,357 Moraw and Schadlich disclose a method to enable the multiplexing of holographic images on a single recording medium by using a beveled conical mirror such that the recordings are made at incremental angles between the object beam and the reference beam. This angle between the reference beam and the plane of the recording medium is referred to as the ‘azimuth angle’. In U.S. Pat. No. 5,696,613 Redfield and Trisned disclose a method of multiplexing pages of data holographically at locations in a thin storage media using differing planes of incidence for the reference beam to interfere with the object beam by which a deflection system deflects the reference beam.
In U.S. Pat. No. 6,862,121 B2 Psaltis and Co-inventors disclose an apparatus which uses a frequency doubled Q-switched Nd:YAG laser to generate reference and signal pulse trains and a CCD camera to record holographically captured time sequenced ultra-fast phenomena which is angular multiplexed in a recording medium. It is necessary to mention that the optical circuit of which this apparatus comprises is highly complex. In U.S. Pat. No. 7,362,482 Kihara discloses a method of multiplexing pages of data using an inline type speckle multiplexed hologram recording and reproducing apparatus in which laser light is introduced into a spatial light modulator and intensity modulated by the spatial light modulator. Interference between the intensity modulated signal light and the reference light is captured in a recording medium. In U.S. Pat. No. 7,710,845 Yoshiyuki and co-inventors describe a holographic recording apparatus that enables the recording of information onto a disc by angle multiplexing of which the disc is a type of photopolymer recording medium.
Amongst the various methods of multiplexing is spatial multiplexing which refers to rotating the recording medium in the plane perpendicular or near perpendicular to the directions of travel of the reference and object light. However, if the direction of polarization of the laser beam can be rotated then this would also achieve spatial multiplexing. There are presently components which enable the direction of polarization to be rotated. Such a component which can be embedded into an apparatus to rotate the direction of polarization of monochromatic light is disclosed by Simony and co-inventors in U.S. Pat. No. 4,579,422. This device uses a liquid crystal composition held between glass plates which rotates the polarization of monochromatic light as a function of applied voltage. An elaborate polarization rotation waveguide device is disclosed in U.S. Pat. No. 5,243,669
The apparatus of this invention requires components that deflect the path by which laser light is traveling when this path is in the transverse direction to the plane of the front surface of the component. These components are known as switchable diffractive elements or switchable optical components and are disclosed in U.S. Pat. No. 5,937,115 by Domash and also in U.S. Pat. No. 6,567,573 by Domash. This invention also requires an advanced Q-switched Nd:YLF/phosphate Glass Laser. The theoretical blueprint for these lasers is described in the following article ‘DESIGN OF A FAMILY OF ADVANCED Nd:YLF/PHOSPHATE GLASS LASERS FOR PULSED HOLOGRAPHY’ by Grichine; Ratcliffe and Rodin published in SPIE proceedings Volume 3358 pages 194 to 202. Another development in Laser Science and technology that also could be used to provide the coherent light source for this invention are optically pumped semiconductor lasers. These devices are described in U.S. Pat. No. 7,447,245 by Caprara and Co-inventors and U.S. Pat. No. 7,991,026 by Caprara. These devices would also be ideal providing they can be Q-switched.